rules

Instruction file imported from doraemonkeys/sloc-guard (.cursor/rules/rules.mdc). Copyright stays with the author.

• Explain "Why", not "What": Use comments to explain design rationale, business logic constraints, or non-obvious trade-offs. Code structure and naming should inherently describe the "what."
• Principle of Least Surprise: Design logic to be intuitive. Code implementation must behave as a developer expects, and functional design must align with the user's intuition.
• Design for Testability (DfT): Favor Dependency Injection and decoupled components. Define interfaces via Traits to allow easy mocking, and prefer small, pure functions that can be unit-tested in isolation.
• Prefer Static Dispatch: Use Generics and Trait Bounds over Trait Objects (e.g., Box<dyn Trait>) to leverage monomorphization and compiler optimizations, unless runtime polymorphism is strictly necessary.
• Make Illegal States Unrepresentable: Use Enums with associated data to model state machines, rather than Structs with many optional fields.
• No Backward Compatibility: Prioritize first-principles domain modeling and logical orthogonality; favor refactoring core structures to capture native semantics over adding additive flags or 'patch' parameters.
• Hard Requirement: Project CI enforces a 90% minimum test coverage.
• Separate Tests from Code: Tests in *_tests.rs; prefer #[path="..."] mod ...; over pub(crate) for test access.